CN110591685A - A kind of in-situ self-generated micro-foam diversion acidification liquid, acidification diversion method and application - Google Patents

Abstract

The invention provides an in-situ self-generated microfoam diverting acidification solution, acidification diversion method and application, the diversion acidification solution comprises: hydrochloric acid 15%-20%, corrosion inhibitor 0.2%-1.0%, anti-swelling agent 0.5%-1.0% %, surfactant 0.5%‑1.0%, the balance is water, no gas is introduced; the surfactant is fatty alcohol polyoxyethylene polyoxypropylene ether, nonylphenol polyoxyethylene ether or polyethylene glycol perfluorobutyric acid ester. CO ₂ micro-foams are spontaneously formed in situ in the formation without gas injection equipment, foam generators, etc., which greatly simplifies the construction procedures of foam acidification and reduces construction costs.

Description

A kind of in-situ self-generated micro-foam diversion acidification liquid, acidification diversion method and application

technical field

The invention belongs to the field of oil and gas exploitation, and in particular relates to an in-situ self-generated microfoam diverting acidizing fluid, an acidizing diverting method and its application.

Background technique

Acid fracturing technology is one of the important means for the exploration and development of carbonate reservoirs, increasing production and stabilizing production. For carbonate reservoirs, during the acidizing process, a large number of acid-eroded wormholes are generated due to the reaction of acid and reservoir rocks, which further increases the permeability difference between reservoirs and makes the carbonate reservoirs turn. It is more difficult than sandstone reservoirs. Traditional acidification diversion technology, the conventional acidification diversion fluid system usually preferentially penetrates the high permeability part or large pores of the reservoir. When ordinary hydrochloric acid acidifies the carbonate rock formation, some main channels are easy to form in the bedrock, and the acid will flow along These channels are further acidified by flow, and it is difficult to acidify other rock formations, so it is usually difficult for acid liquid to act on low-permeability areas or small pores, which are also areas that need to be acted on. Therefore, it is necessary to add a diverting agent to the acid solution to temporarily block the large pores and high-permeability channels, change the flow profile of the acid solution, and allow the acid solution to enter the low-permeability area and small pores to achieve a uniform acidification layer. For deep and ultra-deep carbonate reservoirs, this type of reservoir is characterized by deep reservoir burial, high formation temperature, thick pay zone, serious reservoir heterogeneity, high carbonate purity in the matrix, and natural The production rate is very low. During the acid fracturing operation, the effective and uniform distribution of acid liquid in this type of formation is the key to the effect of matrix acidizing treatment. Due to the heterogeneity of the formation, the acid liquid tends to point to the high-permeability layer, and it is necessary to use diverting acid and other technologies to effectively treat the low-permeability layer.

At present, the main acidizing shunting technologies include: mechanical shunting technology, MAPDIR shunting technology, chemical particle shunting technology, thickening acid shunting technology, viscoelastic surfactant shunting technology, foam acidizing shunting technology, etc. Among them, foam acidizing technology has a good application prospect in oil wells with prominent interlayer and intralayer contradictions due to its low density, small fluid loss, and remarkable retarding effect.

The on-site construction of the foam acidification process requires a lot of additional equipment, such as special nitrogen generators, foam generators, etc., which makes the construction cost of a single well relatively high, thus greatly limiting its extensive application in oilfield sites.

Contents of the invention

Aiming at the problems existing in the prior art of carbonatite reservoirs, the present invention provides an in-situ self-generated micro-foam diversion acidizing fluid and an acidification diversion method and application, in which _CO2 micro-foams are spontaneously formed in situ in the formation without gas injection equipment , foam generator, etc., which greatly simplifies the construction procedure of foam acidification and reduces construction costs.

The present invention is achieved through the following technical solutions:

An in-situ self-generated microfoam diverting acidification solution, according to mass percentage, comprising: hydrochloric acid 15%-20%, corrosion inhibitor 0.2%-1.0%, anti-swelling agent 0.5%-1.0%, surfactant 0.5%- 1.0%, the balance is water, no gas is introduced; the surfactant is fatty alcohol polyoxyethylene polyoxypropylene ether, nonylphenol polyoxyethylene ether or polyethylene glycol perfluorobutyrate.

Preferably, the corrosion inhibitor is utolopine, rhodine or tannic acid.

Preferably, the anti-swelling agent is ammonium chloride, guanidine salt, quaternary ammonium salt or zirconium oxychloride.

An acidizing and diverting method based on the diverting acidizing fluid, adopting a multi-stage injection method, first injecting the diverting acidizing fluid slug into the formation, and then injecting the main acid liquid slug, the main acid liquid includes hydrochloric acid.

Preferably, the main acid liquid also includes one or more of the following additives: corrosion inhibitors, iron ion stabilizers, anti-residual acid emulsifiers, clay anti-swelling agents, drainage aids and organic plug-removing agents.

The acidizing diversion method of the diverting acidizing fluid includes injecting the diverting acidizing fluid as the main acid fluid into the formation.

The application of the diverting acidizing fluid in carbonate formations.

Compared with the prior art, the present invention has the following beneficial technical effects:

The diverting acidizing fluid of the present invention, after being injected into the formation, reacts chemically with the carbonate rock core to generate supercritical _CO2 gas, and under the action of the surfactant, _CO2 micro-bubbles are spontaneously formed in the formation in situ. This is mainly because within a certain temperature and pressure range, the acid liquid expands, the kinetic energy of the surfactant molecules increases, and the distance between molecules increases, which makes it easier for the surfactant molecules to break free from the shackles of water and reach the liquid surface, making the liquid surface The number of adsorbed surfactant molecules increases, which further reduces the surface tension of the liquid film, which is conducive to foaming. In addition, the nonpolar tails of surfactants are stretched in the supercritical _CO2 phase, and the polar heads are aggregated into polar cores, and water molecules dissolve in the cores to form a thermodynamically stable state. And supercritical _CO2 has weak van der Waals force and low dielectric constant, so most hydrophilic or hydrophobic surfactants are insoluble in _CO2 , especially ionic surfactants, so nonionic surfactants are used Type surfactant, in the supercritical state, has good gas solubility, and can make the CO ₂ foam acid system more stable. _CO2 is a non-polar molecule with small intermolecular force, low melting and boiling point, large bond energy, strong interatomic force, and high thermal stability. It has high solubility in oil and water, high density, high critical temperature, and is not affected by conditions such as well depth temperature, pressure, and formation water salinity, and has a wide range of applications. Under specific temperature and pressure conditions, that is, the supercritical state exhibits different properties from those under conventional pressure and temperature conditions. When _CO2 is in a supercritical state, its properties will change, its density is close to that of liquid, its viscosity is close to that of gas, and its diffusion coefficient is 100 times that of liquid, so it has a stronger dissolution network and is better able to drive out from the formation. instead of crude oil. On the other hand, the gaseous state can enter many spaces that solvents cannot enter, thereby expanding the oil sweep area. The self-generating foam system has the effect of "blocking the big but not the small", which can improve the recovery rate of the middle and low permeability layers. Moreover, the flow resistance of the foam fluid is very high, and the gas generated by the system can also produce a vapor resistance effect, blocking the original flow channel, making the injection fluid diverted into the medium and low permeability channels, increasing the volumetric sweep coefficient of the system, and forcing the unused Crude oil was also displaced. In addition, the dissolution of carbon dioxide in crude oil will cause crude oil to swell, reduce viscosity, change density, and reduce interfacial tension. When the dissolved gas in the crude oil is saturated, the viscosity of the crude oil can be greatly reduced and the oil washing efficiency can be improved. The surfactant added to the self-generating foam system can reduce the interfacial tension of oil and water, reduce the capillary force, reverse the wettability of the rock surface from oil-wet to water-wet, and drive away the oil film adhered to the rock surface, thereby improving the oil washing efficiency .

The invention directly utilizes the conventional acidification acidification process without gas injection equipment, greatly simplifies the construction procedure of foam acidification, reduces construction cost, enhances the applicability of foam acidification, and the foam acidification technology can be popularized. In the process of acidification and acid fracturing, CO ₂ is formed in situ, and the deflection and slow acidification of foam are used to achieve the purpose of uniform acid distribution, effective length of acid-etched cracks and flow conductivity of acid-etched cracks after acid fracturing. On the other hand, it also has a drainage effect, and the generated gas increases the elastic driving energy of the formation fluid, which facilitates the flow of crude oil in the formation, improves production capacity, and at the same time serves the purpose of rapid flowback of acid liquid.

Detailed ways

The present invention will be further described in detail below in conjunction with specific embodiments, which are explanations of the present invention rather than limitations.

The diverting acidification solution of in-situ self-generated microfoam according to the present invention comprises: 15%-20% of hydrochloric acid, 0.2%-1.0% of corrosion inhibitor, 0.5%-1.0% of anti-swelling agent, and surfactant 0.5%-1.0%, the balance is water. The surfactant is fatty alcohol polyoxyethylene polyoxypropylene ether, nonylphenol polyoxyethylene ether or polyethylene glycol perfluorobutyrate.

The corrosion inhibitor is utolopine, rhodine or tannic acid; the anti-swelling agent is ammonium chloride, guanidine salt, quaternary ammonium salt or zirconium oxychloride.

According to formation conditions, the diverting acidizing fluid of the present invention can be used alone or in combination with main acid fluid. In terms of mass percentage, the main acid solution includes 15%-20% hydrochloric acid, and the main acid solution also contains one or more of the following additives: corrosion inhibitor 0.2%-1%, iron ion stabilizer 0.5%-1 %, 0.5%-1% of anti-residual acid emulsifier, 0.5%-1% of clay anti-swelling agent, 0.2%-0.5% of drainage aid and 1%-2% of organic plug-removing agent, and the balance is water.

Depending on the formation conditions, two injection techniques can be used:

A. Foam slug diversion acidification: multi-stage injection is adopted, and each stage is first injected with a slug of diverting acidification fluid to temporarily block the high-permeability layer, and then inject the main acid slug to deblock and acidify the low-permeability layer . Realize that the acid liquid enters rock formations with different permeability, and at the same time, use foam acid with high apparent viscosity and high carrying capacity to flow back the acidified solid particles and residual liquid, reduce secondary damage, and avoid other diversion methods Damage to the formation and incomplete flowback of residual liquid.

B. Foam acid diversion acidification: pump the steering acidizing fluid as the main acid fluid, that is, only inject the steering acidizing fluid. Surfactants are added to the conventional acidizing fluid to form a homogeneous system. During the continuous injection into the formation, a foam acid with acidizing fluid as the continuous phase and air bubbles as the dispersed phase is formed. The acidizing fluid is divided by utilizing the splitting characteristics of the foam acid. The advantage of the process is that the diversion effect is good. It can effectively solve the problem of the arrangement of acidizing fluid in heterogeneous reservoirs and the problems existing in conventional acidizing of heterogeneous reservoirs. Foam diversion acidification generally has higher permeability in high water-bearing layers. If the early water blocking effect is not ideal, and some water outlet channels are not effectively blocked, according to the principle of "blocking large but not small" foam, it can prevent excessive flow of water outlet channels. acidification. The proportion of gas in the foam system is large, the self-expansion is high, it is easy to energize and flow back, and there is almost no secondary damage. The foam can form a complex membrane surface in the roaring channel, prevent the wall surface from contacting the liquid, reduce the water-sensitive pollution of the formation, and at the same time reduce the loss of the acidizing fluid to the formation.

Residual acid flowback process:

Shut down the well for 3 hours and blow out. Wash the well with active water and flow back the residual acid until all the acid liquid entering the well is discharged.

According to the energy level of the reservoir, two technologies of wellhead blowout and foam lift flowback are adopted respectively. For wells with high reservoir pressure, good permeability and high production potential, after foam acidification reformation, the wellhead blowout flowback technology is used to flow back fluid in the wellbore; for wells with poor permeability and low reservoir productivity , use the foam lifting and flowback method to discharge acid. Foam lift flowback has a very significant protective effect on reservoirs with poor permeability, low formation pressure and reservoir sensitivity.

Aiming at the vertical heterogeneity and pollution degree difference of the carbonate reservoir, the present invention adopts the diverting acidizing fluid system, and generates CO ₂ through the chemical reaction between the diverting acidizing fluid system and the carbonate core during the acidizing acid fracturing process Gas (existing in supercritical state), under the action of surfactant, spontaneously forms CO ₂ micro-foam fluid in situ in the formation, and uses the deflection and slow acidification of foam to achieve uniform acid distribution and effective length of acid-etched fractures and the purpose of the conductivity of the acid-etched fractures after acid fracturing, and at the same time use the low surface tension characteristics of the diverted acidizing fluid to quickly and efficiently return the residual fluid to the formation, and improve the flowback of the acidizing residual fluid in low-permeability and low-pressure reservoirs Efficiency, reducing the damage of residual fluid to low permeability reservoirs, and restoring the productivity of oil wells to the maximum extent.

construction steps

1. When moving to the well, take out the original well for inspection, check the data, and clean the injection string.

2. Construction injection parameters

(1) Injection method: graded injection/direct injection.

(2) Injection pressure: lower than the fracture pressure of the oil layer, graded injection is ≤15Mpa, and direct injection is ≤30Mpa.

(3) Injection speed: It is determined according to the water absorption of the injection well. During construction, it is required to inject the pressure steadily. Inject as much displacement as possible to increase the penetration distance of the plugging solution.

3. Acidification depressurization increase injection construction:

(1) Lower the acidizing drilling tool.

(2) Connect the surface pipeline, test the pressure of the wellhead and the surface pipeline to 30MPa, and check that it is qualified if it does not puncture or leak.

(3) Preparation of acidification solution.

(4) Use active water to positively circulate to the annulus to return water.

(5) Inject the pre-acid solution (the diverting acidizing solution of the present invention), the dosage is 0.5m ³ +0.6m ³ active water per meter of oil layer, the pressure is ≤20MPa, and the well is shut in for 60 minutes.

(6) Inject the main acid solution, the dosage is 1-2m ³ per meter of oil layer.

(7) After injecting 6m ³ of acid liquid, the pressure is less than 20MPa, the displacement is as large as possible, and the well is shut down for 12 hours.

(8) Close the casing gate, positively squeeze 3.9m ³ of active water, pressure ≤ 20MPa, wash the well with large displacement reverse circulation until the reaction residual acid is completely returned.

or:

(5) Inject the diverting acidizing fluid of the present invention, with an amount of 5-8 m ³ per meter of oil layer.

(6) Close the casing gate, positively squeeze 3.9m ³ of active water, pressure ≤ 20MPa, wash the well with large displacement reverse circulation until the reaction residual acid is completely returned.

4. After acidification, calculate the water absorption index at four different pressures (pressure level 2MPa) above the starting pressure, and squeeze 5m ³ of water respectively. The starting pressure is less than 15MPa, and the water absorption is greater than 50L/min. If it is unqualified, report it to the technical management department in time to determine the next step. After the water absorption is completed, inject 20m ³ of active water into the formation.

5. Press the seat seal. Open the casing gate, use a cement truck to press 14MPa, 16MPa, and 18MPa respectively from the oil pipe, and stabilize the pressure for 5 minutes each. If the pressure drop is not greater than 2MPa, it is qualified.

6. Install the wellhead according to the standard, test the pressure to 20MPa without leakage, and connect the ground water injection pipeline well. The operation team packed up the well site and moved away from the well site.

Specific examples are as follows

Example 1

The indoor simulation experiment of an oilfield core is taken as an example to illustrate.

Flow experiments using carbonate cores with different permeability simulate the fluid permeability in the reservoir due to reservoir heterogeneity under formation conditions. The core is from the Longwangmiao Formation core in Anyue, Sichuan, numbered 1#. Core 1#: diameter 2.36cm, porosity 30.5%, permeability 698×10 ^-3 μm ² , simulated temperature 60°C, pressure 1MPa.

Preparation of acid solution: (1) In-situ self-generated micro-foam turning acidification solution (pre-acid solution) includes: 15% hydrochloric acid, 0.5% fatty alcohol polyoxyethylene polyoxypropylene ether, 0.2% corrosion inhibitor uropine, 0.5% anti-swelling agent ammonium chloride, the balance is active water. (2) The main acid solution includes: 20% hydrochloric acid, 0.5% corrosion inhibitor utolopine, 0.5% clay anti-swelling agent, 0.5% anti-residual acid emulsifier, 0.5% drainage aid, 0.5% iron ion stabilizer, 1% organic plug-removing agent, the balance is active water. (3) The post-acid solution includes: 8% hydrochloric acid, 0.5% corrosion inhibitor, 0.3% drainage aid, and the balance is active water. The composition of each acid solution is shown in Table 1.

The acid liquid is injected in stages, that is, the pre-acid liquid is injected first, then the main acid liquid is injected, and the post-acid liquid is injected finally. Measure the change in permeability of the core before and after acidification. The experimental results show that the permeability of the core reaches 3420×10 ^-3 μm ^{2 ,} which is 4.9 times of the initial permeability, which achieves good results.

The composition of each acid solution in Table 1

Example 2

The indoor simulation experiment of an oilfield core is taken as an example to illustrate.

Flow experiments using carbonate cores with different permeability simulate the fluid permeability in the reservoir due to reservoir heterogeneity under formation conditions. The core is from the Longwangmiao Formation core in Anyue, Sichuan, numbered 2#. 2# core: diameter 2.68cm, porosity 28.7%, permeability 590×10 ^-3 μm ² , simulated temperature 60°C, pressure 2MPa.

Prepare the acid solution (the turning acidification solution of self-generated microfoam in situ in the present invention), including: 18% hydrochloric acid, 0.8% polyethylene glycol perfluorobutyrate, 0.3% corrosion inhibitor tannic acid, 0.7% anti-swelling agent two Zirconium oxychloride, the balance is active water. See Table 2 for the composition of the diverting acidification solution of in-situ self-generated microfoam.

The diverting acidizing liquid of the self-generated microfoam in the present invention is directly injected as the main acid liquid, and the change of the permeability of the rock core before and after acidizing is measured. Experimental results show that the permeability of the core reaches 4423×10 ^-3 μm ² , which is 7.5 times of the initial permeability, achieving good results.

Table 2 Composition of diverting acidification fluid of self-generated microfoam in situ

components content Hydrochloric acid (wt%) 18 Surfactant (wt%) 0.8 Corrosion inhibitor (wt%) 0.3 Anti-swelling agent (wt%) 0.7 Active water (wt%) 80.2%

Example 3

The indoor simulation experiment of an oilfield core is taken as an example to illustrate.

Flow experiments using carbonate cores with different permeability simulate the fluid permeability in the reservoir due to reservoir heterogeneity under formation conditions. The core is from the Longwangmiao Formation in Anyue, Sichuan, numbered 3#. 3# core: diameter 2.46cm, porosity 31.4%, permeability 627×10 ^-3 μm ² , simulated temperature 60°C, pressure 2MPa.

Preparation of acid solution (in-situ self-generated microfoam turning acidification solution of the present invention), including: 20% hydrochloric acid, 1.0% fatty alcohol polyoxyethylene polyoxypropylene ether, 1.0% corrosion inhibitor rhodin, 1.0% anti-swelling agent guanidine salt , and the balance is active water. Table 3 shows the composition of the diverting acidification solution for the in-situ self-generated microfoam.

The diverting acidizing liquid of the self-generated microfoam in the present invention is directly injected as the main acid liquid, and the change of the permeability of the rock core before and after acidizing is measured. Experimental results show that the permeability of the core reaches 4201×10 ^-3 μm ² , which is 6.7 times of the initial permeability, achieving good results.

Table 3 Composition of diverting acidification fluid of self-generated microfoam in situ

Example 4

The dissolution rate of soluble matter between the acid liquid and the formation is an important index to measure the performance of the acid liquid. Using foam acid to react with carbonate cuttings, calculate the amount of dissolution, and evaluate the excellent performance of the acid solution. The carbonate cuttings sampled from Tahe Oilfield were passed through a 18-mesh sieve, and after drying, a certain quality of cuttings was weighed. Prepare 50 mL of diverting acidification solution: 17% hydrochloric acid, 0.5% nonylphenol polyoxyethylene ether, 0.5% uropine, 0.5% ammonium chloride, and the balance is active water. The composition is shown in Table 4. Pour the prepared diverting acidification solution into the airflow foaming device, and fill it with _CO2 gas at a flow rate of 95ml/min to make the foam acid liquid reach the state of sufficient foaming; add the weighed Carbonate cuttings, while adjusting the airflow rate to 45ml/min to maintain the foaming state of the foam acid in the device. After reacting for a period of time, the carbonate cuttings were cleaned, dried and weighed to calculate the amount of dissolution.

The dissolution rate of the acid-rock reaction is calculated based on the quality difference of the rock sample before and after the reaction. The calculation formula used is as follows, η=(m1-m2)/m1×100%, where η is the dissolution rate of the rock sample, and m1 is the Rock sample quality, m2 is the rock sample quality after reaction.

Table 4 Composition of diverting acidizing fluid

components content Hydrochloric acid (wt%) 17 Surfactant (wt%) 0.5 Corrosion inhibitor (wt%) 0.5 Anti-swelling agent (wt%) 0.7 Active water (wt%) 81.3%

Through experiments, the reaction at room temperature is 60 minutes, and the corrosion rate is as high as 87%, which has a good effect.

Claims (7)

1. an in-situ self-generated micro-foam diversion acidification solution, characterized in that, according to mass percentage, comprising: hydrochloric acid 15%-20%, corrosion inhibitor 0.2%-1.0%, anti-swelling agent 0.5%-1.0%, The surfactant is 0.5%-1.0%, the balance is water, and no gas is introduced; the surfactant is fatty alcohol polyoxyethylene polyoxypropylene ether, nonylphenol polyoxyethylene ether or polyethylene glycol perfluorobutyrate. 2. the diverting acidification liquid of in-situ self-generated micro-foam according to claim 1, is characterized in that, corrosion inhibitor is uropin, rhodine or tannic acid. 3. The diverting acidification fluid of in-situ self-generated microfoam according to claim 1, characterized in that the anti-swelling agent is ammonium chloride, guanidinium salt, quaternary ammonium salt or zirconium oxychloride. 4. A method for acidizing diversion based on the diverting acidizing fluid described in any one of claims 1-3, characterized in that, the method of multi-stage injection is used to inject the fluid described in any one of claims 1-3 into the formation earlier. Turn to the acidizing fluid slug and then inject the main acid slug, which includes hydrochloric acid. 5. The method according to claim 4, characterized in that, the main acid solution also includes one or more of the following auxiliary agents: corrosion inhibitor, iron ion stabilizer, anti-residual acid emulsifier , Clay anti-swelling agent, drainage aid and organic plugging remover. 6. An acidizing diversion method based on the diverting acidizing fluid according to any one of claims 1-3, injecting the diverting acidizing fluid as the main acid fluid into the formation. 7. The application of the diverting acidizing fluid described in any one of claims 1-3 in carbonate formations.